In turbochargers for internal combustion engines, it is aerodynamically advantageous to first let the engine exhaust gas flow inwards through an entry volute or through guide vanes over the complete periphery while imparting the necessary swirl and subsequently, after deflection, through the axial turbine.
An axial turbine having a radial flow turbine guide apparatus of the type mentioned above is shown in the European patent application No. 0 093 462 published Nov. 9, 1983 (FIG. 2).
In this device, the inner wall of the gas deflection duct located between the turbine guide apparatus and the turbine rotor blades is fixed and immovable. Because of gas friction on this wall, a loss of swirl occurs. Due to the high peripheral gas velocity, which increases in the radially inward direction, this inner wall of the gas deflection duct causes relatively high frictional losses. The isentropic efficiency of the turbine is reduced due to this by an additive 2% to 5% approximately.